This invention relates in general to wireline operations in oil and gas wells, and in particular to a system for mounting the winch of a wireline.
There are two main types of wireline operations, slick line and conductor cable. In slick line operations, wireline tools are lowered into a well and manipulated to perform various functions, without the use of electrical current. In conductor cable operations, electrical current is passed to an instrument or tool downhole. The downhole tool may perform various operations, as well as provide surface indications of downhole well characteristics.
Both of these types use a power driven drum or winch wrapped with the wireline and located in a unit on the drill rig, or in the case of land rigs, normally a truck off to the side of the drill rig. The wireline is reeved through a lower sheave, which is tied to the rig or well head, then over an upper sheave, which may be supported by the well head equipment or by the rig, and down into the well conduit, which may be tubing, casing or drill pipe. Often, stringing the wireline through the sheaves places the wireline in an inconvenient position for other work going on the rig, particularly offshore rigs and platforms.
A more serious problem occurs when the drill pipe must be supported by travelling blocks when the wireline operation is being performed through the drill pipe. If it is necessary to move the drill pipe up or down while the downhole wireline tool remains stationary, line must be fed in or out simultaneously to avoid changing the tension in the line, or the line must be clamped at the top of the well.
The prior art wireline system of rigging up is also a problem in the case of offshore drilling rigs that float. In these types of rigs, the drill pipe or well conduit is substantially isolated from wave action. When not supported by the derrick, the well conduit will be supported by the subsea well head control equipment. While the drill pipe is being supported by the blocks, a heave compensator secured to the top of the blocks acts as a shock absorber to remove most of the wave action, so that the drill pipe will not move up and down with the drilling rig.
In a wireline operation on a floating rig, the upper sheave can be generally isolated from wave action by connecting it to the top of the drill pipe. The power driven drum, however, will be located on the rig and thus subject to wave action.